An ongoing problem in clinical otology has been the difficulty in identifying patients with endolymphatic hydrops (ELH) in the early stages when the presentation of the classic triad of tinnitus, fluctuating hearing loss, and episodic vertigo is incomplete. Consequently, delays in diagnosis and subsequent treatment lead to progressive sensorineural hearing loss, recurring vertigo and eventually deafness. Most cases of ELH are idiopathic and thus such patients are diagnosed with what is termed Meniere's disease. The long term goal of this investigation is to identify patients in the early stages of Meniere's disease, thus permitting early treatment. The symptoms with which Meniere's patients present are commonly seen in other diseases, making an accurate diagnosis difficult to obtain. Therefore, proper identification of patients early in the course of the disease requires indices which are sensitive to subtle changes in cochlear function and which are also specific to the pathology of endolymphatic hydrops. The specific aim of this project is to use the guinea pig model of ELH to derive an index sensitive and specific to endolymphatic hydrops from measures which reflect cochlear mechanics such as otoacoustic emissions and electrocochleography. A new nonlinear systems identification (NLSI) technique will be used to measure cochlear mechano-electric transduction. The index will be derived from conventional electrocochleography measures (i.e. SP/AP ratio, N1 latency) and otoacoustic emissions as well the NLSI measures. Once such an index has been developed in our animal model, we will apply it to measurements made in human patients.